Fuel cell power systems convert a fuel and an oxidant (reactants) to electricity. One type of fuel cell power system employs a proton exchange membrane (PEM) to catalytically facilitate reaction of the fuel (such as hydrogen) and the oxidant (such as air or oxygen) to generate electricity. Water is a byproduct of the electrochemical reaction. The PEM is a solid polymer electrolyte that facilitates transfer of protons from an anode electrode to a cathode electrode in each individual fuel cell of a stack of fuel cells normally deployed in a fuel cell power system.
In the typical fuel cell assembly, the individual fuel cells have fuel cell plates with channels, through which various reactants and cooling fluids flow. Fuel cell plates may be unipolar or bipolar, for example. A bipolar plate may be formed by combining unipolar plates. The oxidant is supplied to the cathode electrode from a cathode inlet header and the fuel is supplied to the anode electrode from an anode inlet header. Movement of the water byproduct from the channels to an outlet header is typically caused by the flow of the reactants through the fuel cell assembly. Boundary layer shear forces and a pressure of the reactant aid in transporting the water through the channels until the water exits the fuel cell through the outlet header.
A membrane-electrode-assembly (MEA) is disposed between successive plates to facilitate the electrochemical reaction. The MEA includes the anode electrode, the cathode electrode, and an electrolyte membrane disposed therebetween. Porous diffusion media (DM) are positioned on both sides of the MEA to facilitate a delivery of reactants for the electrochemical fuel cell reaction.
When initiating the electrochemical fuel cell reaction in the fuel cell stack, it is typically desirable to provide the hydrogen fuel in such a manner to cause the individual fuel cells to receive the hydrogen in the active areas thereof at substantially the same time. However, the inlet header typically fills with hydrogen in such a manner that causes fuel cells closest to a hydrogen inlet of the inlet header to be the first fuel cells to receive the hydrogen. Conversely, the fuel cells that are farthest from the hydrogen inlet of the inlet header are the last fuel cells to receive the hydrogen.
As the hydrogen flows into the active areas of the fuel cell plates, a localized voltage rise may be measured. When an electrical load is applied to the fuel cell stack, the voltage rise generates a current that is driven through the remaining fuel cell plates of the fuel cell stack. Fuel cells of the fuel cell stack which do not have a sufficient amount of hydrogen to support the current may experience a localized reversed current, thereby resulting in electrode carbon corrosion. Delaying the start of the electrochemical fuel cell reaction until such time as all the fuel cells are supplied with hydrogen typically results in an undesired emission of hydrogen through the exhaust header of the fuel cell stack.
Various techniques have been employed to simultaneously provide hydrogen to each of the fuel cells at the start-up of the electrochemical fuel cell reaction in the fuel cell stack. One such technique includes providing an inlet header purge valve such as disclosed in U.S. Patent Application Publication No. 2005/0129999. The purge valve enables the inlet header to be flushed with hydrogen just prior to initiating the electrochemical fuel cell reaction. The purge valve increases a cost of the fuel cell stack and introduces additional moving parts to the system.
An alternative technique has employed a plurality of fluid passages to form an external header that supplies the hydrogen to distributed locations within the inlet header of the fuel cell stack. U.S. Pat. No. 6,924,056 and U.S. Patent Application Publication Nos. 2005/0118487 and 2006/0280995 generally illustrate such a technique. The external header may be difficult to seal against the fuel cell stack, and increases a cost and overall size of the fuel cell stack.
It would be desirable to produce a cost effective inlet header insert for a fuel cell stack that facilitates a substantially simultaneous delivery of a hydrogen fuel to each fuel cell in the fuel cell stack at the initiation of an electrochemical fuel cell reaction.